1. Field of the Invention
The present invention relates generally to magnetic recording heads used in disk drives and specifically to a method for testing the susceptibility of magnetic recording heads to corrosion.
2. Description of the Background Art
Contemporary disk drives have at least one disk for storing digital information and at least one recording head for writing and reading digital information to the disk. The disk and head both comprise materials which are susceptible to corrosion. The read back sensor on the recording head in particular is constructed with materials which can be susceptible to corrosion. The materials in the read back sensor of the head are usually covered with a thin layer of diamond like carbon (DLC) to protect against corrosion. This DLC coating is effective for corrosion protection, but is not perfect. Accordingly one of the challenges when designing and constructing magnetic recording heads is to properly evaluate the susceptibility of the materials in heads to corrosion and also the effectiveness of corrosion protection measures.
One method of testing the corrosion performance of recording heads is to build a disk drive using the heads of interest. The disk drive is then subjected to long term testing. This testing can be done at ambient conditions or in an accelerated corrosion environment of high temperature and high humidity. Very accelerated conditions can be achieved by additionally placing the disk drive in a corrosive mix of gases such as chlorine, hydrogen sulfide, etc. This method of utilizing the finished disk drives for corrosion testing is very expensive and quite slow. Also there is usually considerable uncertainty in relating results from aggressively accelerated tests to actual performance when the disk drive is in a normal use environment.
Another method of testing the corrosion performance of recording heads involves an accelerated test at the component level. In this method individual heads are placed in a corrosion testing chamber having elevated temperature and humidity. Optionally corrosive gases such as chlorine and hydrogen sulfide can also be introduced into the testing chamber. Another optional technique is to dip the heads in a saline solution before testing. The component level method is less expensive and much faster than the disk drive method. However the corrosion results from this component method correlate poorly with the results from normal operation of the disk drive. This is because the recording head during component level testing is exposed to different chemical and environmental stresses than during normal operation of a disk drive.
There is a need for a method of corrosion testing of recording heads at the component level which is fast and inexpensive and also indicates more accurately the performance in the disk drive.
One embodiment of the present invention provides for a corrosion testing method for recording heads which is fast and inexpensive. The method is based on testing components but the results correlate well with corrosion testing of recording heads inside disk drives. The method includes applying a cobalt salt to the recording head; measuring the resistance of the read element in the recording head; subjecting the recording head to elevated temperature and humidity; making a second resistance measurement of the read element; and finally, comparing the two resistance measurements. An example of one cobalt salt which may be used is cobalt sulfate. The cobalt salt may be applied to the recording head by dipping the head into a solution of the salt, by evaporating the salt onto the head, or by applying a slurry of the salt mixed with a lubricant.
Other aspects and advantages of the present invention will become apparent from the detailed description along with the drawing illustrating by way of example the principles of the invention.